In recent years, a white LED has been brought to attention as a white lighting light source exhibiting high efficiency as well as high reliability, and has already been utilized partly as a small-size low electric power light source. It is commonly known that this kind of LED is a LED in which a blue LED element is covered by a mixture of a yellow phosphor and a transparent resin, and a white LED and a phosphor used for the white LED with this method are disclosed (refer to Patent Documents 1-3).
However, a blue light tends to deteriorate a resin since energy of the blue light is large. Therefore, the resin loses the color by using the white LED having the above-described structure for long duration, whereby the color tone is also changed. Further, in recent years, though there is a move to introduce the development of a white lighting light source by employing a high-energy LED element, the resin is seriously deteriorated in this case since a limited area is exposed to extremely large energy blue light, whereby change of an emission color is caused in an extremely short period of time. There was also a problem such that the emission color tone was shifted to the yellow side, since a heat discharge property of a resin-molded element is poor, whereby temperature rise is easily generated.
(Patent Document 1) Japanese Patent O.P.I. Publication No. 10-163535
(Patent Document 2) WO98/05078; descriptive literature
(Patent Document 3) Japanese Patent O.P.I. Publication No. 2002-43624